Hierarchical N-doped C/Fe3O4 nanotube composite arrays grown on the carbon fiber cloth as a bioanode for high-performance bioelectrochemical system

Three-dimensional (3D) nano-structure materials with a large bacterial accessible specific area have emerged as promising electrode materials for bioelectrochemical systems (BESs), achieving high bioelectricity outputs. However, it remains a challenge that biofilms with increased thickness inhibit substrate diffusion into the 3D nano-structure during long-term operation of BESs, causing a reduction in bioenergy output. Herein, an innovative ordered 3D nano-structure electrode was fabricated by growing self-supported N-doped C/Fe 3 O 4 -nanotube composite arrays onto carbon fiber cloth ( [email protected] /Fe 3 O 4 ), using template-based deposition coupled with thermal reduction/carbonization methods. The fabricated [email protected] /Fe 3 O 4 electrode was applied as a bioelectrode in a conventional three-electrode BES and as an anode in microbial fuel cell (MFC), while their capacity to improve bioelectricity generation was assessed. Results indicate that the hierarchical N-doped C-coated nanotube arrays not only significantly enhanced conductivity and areal capacitance of the electrode, but also reduced its charge transfer resistance and provided the 3D open nano-structure with excellent biocompatibility for microbial colonization and internal diffusion of the culture substrate. Consequently, a high maximum current density (4.11 mA/cm 2 ) and coulombic efficiency (~89%) was obtained from the [email protected] /Fe 3 O 4 electrode after about 3 months of BES operation, exhibiting higher biocatalytic performance and extracellular electron transfer efficiency than the original carbon fiber cloth (CC, 1.89 mA/cm 2 ). Moreover, MFC equipped with [email protected] /Fe 3 O 4 anode produced a maximum power density of 1.21 ± 0.04 W/m 2 , which was 2.1 times higher than CC (0.58 ± 0.03 W/m 2 ). This study demonstrates the outstanding advantages of [email protected] /Fe 3 O 4 nanotube composite arrays assembled on CC, making it a potential alternative to existing 3D electrodes for high-performance BES applications.